This invention relates to a printing apparatus and a print method, and more particularly, to a printing apparatus having a printhead with a plurality of nozzles to perform printing in accordance with an ink-jet method, and a print method for the apparatus.
A printing apparatus based on the ink-jet method forms an image by directly discharging ink droplets onto a print medium. In an apparatus according to this method, as the number of constituent members used from image input to image formation is less than that required in the electrophotographic printing method or the like, a desired image can be obtained in a stable manner.
However, since the ink-jet method performs printing by discharging very small ink droplets from fine ink-discharge nozzles provided in a printhead, ink discharge failure may occur due to various reasons. For example, (1) if the nozzle is clogged with dust, it does not discharge ink; (2) if print operation is not performed and the printhead is not used for a long period, the volatile component of ink evaporates and the ink viscosity increases, then the nozzle is clogged with the ink, which disturbs ink discharge; (3) if disconnection occurs at a part of heaters, integrated in a high density for film boiling to cause ink discharge, ink discharge fails since heating cannot be made; (4) if a part of ink droplet discharged from an ink discharge orifice may adhere to the discharge orifice and cover the orifice, it disturbs ink discharge. As a result, a white line due to the ink discharge failure occurs in a printed image, which degrades the image quality.
As for this drawback, if the number of nozzles of the printhead is increased to several hundreds or several thousands so as to improve the printing speed, the probability of nozzles in ink-discharge failure status increases in proportion to the increase in the number of the nozzles. Accordingly, this drawback becomes a more serious problem from the viewpoint of quality of printed image.
On the other hand, from the viewpoint of manufacture of printhead, it is necessary to manufacture a faultless printhead which can normally discharge ink from all the nozzles. However, if the number of nozzles is increased to several hundreds or several thousands, the probability of defective nozzles in one printhead increases in proportion to the increase in the number of nozzles, which reduces the yield. That is, there is a problem in the manufacture of printhead to satisfy the economical requirement. Further, even though a faultless printhead can be manufactured, if one of the nozzles has a trouble while the printhead is used, the entire printhead cannot be used.
For example, in a printing apparatus using about four to eight printheads, each having several thousands of nozzles, corresponding to ink colors for full-color printing, it is frequent that some nozzle abnormally operates. Each time abnormal operation occurs at some nozzle, a poor quality image is formed. Such printing apparatus cannot be put into practical use.
To solve these problems, conventionally, various improvements have been made.
For example, a printing method as follows has been proposed to attain excellent image quality even if a nozzle becomes a defective one which does not discharge ink. That is, prior to one print-scanning of the printhead, the defective nozzle is detected, then image data corresponding to the nozzle is removed, and printing is performed in forward-scanning of the printhead. As an image portion corresponding to the defective nozzle is not printed in this printing, a white line remains in the printed image. Next, in backward scanning of the printhead, the printhead is shifted in a print-medium feeding direction for one to several nozzles, or the print medium is conveyed in the print-medium feeding direction such that a normal nozzle is positioned opposite to the white line. Then, the previously-removed image data is sent in an order reversed to that in the forward scanning, and ink discharge is performed by using the normal nozzle. Thus, complementary printing is performed as disclosed in Japanese Patent Application Laid-Open No. 8-25700.
In addition, a particular method to detect a defective nozzle has been proposed as follows. That is, a print medium for detecting ink-discharge status is provided outside an effective printing area by the printhead, and a predetermined pattern is printed while the print medium is conveyed in a print-medium feeding direction at a wide pitch so as to detect a defective nozzle. Next, the printhead is moved away from the printing position, then, an optical reader having a high-resolution CCD camera is moved to the position to read the pattern. Then, a defective nozzle which does not discharge ink is determined based on the read pattern.
Further, it has been also proposed to move the print medium with the printed pattern to the position of the optical reader, and read the pattern at the position by the optical reader.
Further, it has been also proposed to print a pattern on a medium such as a glass disk, then rotate the disk so as to move the pattern to a reading position of an optical reader, and read the pattern by the optical reader.
By adopting these methods, excellent printed images can be obtained.
However, in the above-described methods, the defective nozzle detection cannot be made unless the optical reader is moved to the position where the pattern has been printed or the print medium where the pattern has been printed is moved to the position where the optical reader is situated.
Then, a method for detecting a defective nozzle without moving the optical reader or print medium has been proposed. According to this method, an image forming apparatus may be constructed such that the printhead is stopped at a predetermined position where ink discharged from the printhead can block a light beam from an optical sensor, then ink is discharged to block the light beam, and a defective nozzle is detected from output from the optical sensor. In case of color printer, as a plurality of printheads corresponding to the number of ink colors are mounted, the printheads are sequentially stopped at the predetermined position with high precision for ink discharge.
However, the above-described conventional techniques require a particular operation for detecting a defective nozzle, which greatly reduces the printing speed.
For this reason, it has been proposed not to perform complementary printing but to perform printing using a currently-used printhead during the defective nozzle detection, and to perform the complementary printing after a defective nozzle has been detected. Although this method prevents the reduction of printing speed, it cannot avoid poor quality printing, since it does not perform the complementary printing during the defective nozzle detection.
Accordingly, it is an object of the present invention to provide a printing apparatus and a print method which perform appropriate print control such as complementary printing for printing failure caused by a defective printing element in operation failure status, without reducing a printing speed, by detecting the defective printing element in a realtime manner while reciprocate-scanning a printhead.
According to one aspect of the present invention, the foregoing object is attained by providing a printing apparatus which performs printing by discharging ink onto a print medium while reciprocate-scanning a printhead based on an ink-jet method, having a plurality of printing elements, the apparatus comprising: scan means for reciprocate-scanning the printhead; detection means, provided in a scanning path of the printhead, for detecting ink discharge statuses of the plurality of printing elements of the printhead; test discharge means for controlling operation of the printhead to perform test ink discharge at a position where the detection means is provided, while the scan means reciprocate-scans the printhead; analysis means for detecting ink, discharged by the test discharge means, by using the detection means, and analyzing discharge statuses of the plurality of printing elements of the printhead; and control means for performing print control based on the results of analysis by the analysis means.
Note that the plurality of printing elements of the printhead is arrayed in one line.
Also note that the detection means may be provided at one end of the scanning path of the printhead, or it may be provided outside an area occupied by the printing medium in the scanning path of the printhead.
It is preferable that the detection means includes light emission means for emitting a light beam and photoreception means for receiving the light beam, and the printhead is provided such that ink droplets discharged from the plurality of printing elements block the light beam. Further, it is preferable that the light emission means and the photoreception means are provided such that a light axis of the light intersects an array direction of the plurality of printing elements of the printhead. Further, it is more preferable that the printing apparatus further comprises a slit for limiting a light flux of the light beam entering the photoreception means, in front of the photoreception means.
Further, it is preferable that the printing apparatus further comprises recovery means for performing recovery operation on the printhead, and print means for performing print operation by driving the printhead upon forward scanning of the printhead by the scan means. Further, it is preferable that the printing apparatus comprises specification means for specifying a printing element in discharge failure status among the plurality of printing elements of the printhead, based on the results of analysis by the analysis means; and complementary printing means for performing complementary printing on a printed result by the printing element in the discharge failure status specified by the specification means, by using a printing element which normally operates, upon backward scanning of the printhead.
By the above construction, the control means drives the recovery means based on the results of analysis.
Further, it may be arranged such that the printing apparatus further comprises display means for displaying a message, and if the printing element in the discharge failure status is not recovered from that status even when the control means has driven the recovery means to perform the recovery operation on the printing element a predetermined number of times, the control means displays a message advising a user to change the printhead on the display means. Further, the control means operates the specification means and the complementary printing means based on the results of analysis by the analysis means.
Further, it may be arranged such that the printing apparatus further comprises encoder means for detecting a position of the printhead on the scanning path by the scan means, and ink discharge timing by the test discharge means is based on position information outputted from the encoder means. Further, each of the plurality of printing elements is specified by synchronizing the ink discharge timing with an output signal from the detection means.
Note that it is preferable that the printhead has electrothermal transducers for generating thermal energy to be provided to ink, so as to discharge the ink by utilizing the thermal energy.
According to another aspect of the present invention, the foregoing object is attained by providing a printing method of printing by reciprocally scanning a printhead which has a plurality of printing elements and discharges ink on a printing medium, comprising the steps of: starting to scan the printhead in a predetermined direction; test-discharging ink to a detection unit provided in a scanning path of the printhead; detecting an ink droplet test-discharged by the detection unit; and controlling a print operation during a period of scanning the printhead, based on a detection result in the detecting step, wherein the detecting step detects as to whether or not an ink droplet has been detected, corresponding to each of the plurality of printing elements.
Note that the controlling step performs control such that the printhead prints on the printing medium when scanning the printhead in the predetermined direction, while the printhead complementarily prints on a position, where a printing element was supposed to discharge an ink droplet but it is detected based on the detection result that the printing element did not discharge, of the print medium when scanning the printhead in a direction opposite to the predetermined direction.
In accordance with the present invention as described above, the printing apparatus comprises the detection means, provided at one end of the scanning path of the printhead, for detecting ink discharge statuses of the respective printing elements of the printhead. The apparatus operates the printhead to perform test ink discharge at a position where the detection means is provided while the printhead is scanned, detects the discharged ink by the detection means, analyzes the operation statuses of the respective printing elements of the printhead, and performs print control based on the result of analysis.
The present invention is particularly advantageous since the statuses of the respective printing elements of the printhead can be detected without stopping the printhead or reducing the printing speed.
Accordingly, if a defective printing element in the operation failure status is detected, the printing apparatus performs appropriate print control such as recovery operation or complementary printing.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.